/* alpha    rshift
 *      Copyright (C) 1994, 1995, 1998, 1999,
 *                    2000, 2001 Free Software Foundation, Inc.
 *
 * This file is part of GNUPG.
 *
 * GNUPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GNUPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 *
 * Note: This code is heavily based on the GNU MP Library.
 *	 Actually it's the same code with only minor changes in the
 *	 way the data is stored; this is to support the abstraction
 *	 of an optional secure memory allocation which may be used
 *	 to avoid revealing of sensitive data due to paging etc.
 *	 The GNU MP Library itself is published under the LGPL;
 *	 however I decided to publish this code under the plain GPL.
 */




/*******************
 * mpi_limb_t
 * mpihelp_rshift( mpi_ptr_t wp,	(r16)
 *		   mpi_ptr_t up,	(r17)
 *		   mpi_size_t usize,	(r18)
 *		   unsigned cnt)	(r19)
 *
 * This code runs at 4.8 cycles/limb on the 21064.  With infinite unrolling,
 * it would take 4 cycles/limb.  It should be possible to get down to 3
 * cycles/limb since both ldq and stq can be paired with the other used
 * instructions.  But there are many restrictions in the 21064 pipeline that
 * makes it hard, if not impossible, to get down to 3 cycles/limb:
 *
 * 1. ldq has a 3 cycle delay, srl and sll have a 2 cycle delay.
 * 2. Only aligned instruction pairs can be paired.
 * 3. The store buffer or silo might not be able to deal with the bandwidth.
 */

	.set	noreorder
	.set	noat
.text
	.align	3
	.globl	mpihelp_rshift
	.ent	mpihelp_rshift
mpihelp_rshift:
	.frame	$30,0,$26,0

	ldq	$4,0($17)	# load first limb
	addq	$17,8,$17
	subq	$31,$19,$7
	subq	$18,1,$18
	and	$18,4-1,$20	# number of limbs in first loop
	sll	$4,$7,$0	# compute function result

	beq	$20,.R0
	subq	$18,$20,$18

	.align	3
.Roop0:
	ldq	$3,0($17)
	addq	$16,8,$16
	addq	$17,8,$17
	subq	$20,1,$20
	srl	$4,$19,$5
	sll	$3,$7,$6
	bis	$3,$3,$4
	bis	$5,$6,$8
	stq	$8,-8($16)
	bne	$20,.Roop0

.R0:	beq	$18,.Rend

	.align	3
.Roop:	ldq	$3,0($17)
	addq	$16,32,$16
	subq	$18,4,$18
	srl	$4,$19,$5
	sll	$3,$7,$6

	ldq	$4,8($17)
	srl	$3,$19,$1
	bis	$5,$6,$8
	stq	$8,-32($16)
	sll	$4,$7,$2

	ldq	$3,16($17)
	srl	$4,$19,$5
	bis	$1,$2,$8
	stq	$8,-24($16)
	sll	$3,$7,$6

	ldq	$4,24($17)
	srl	$3,$19,$1
	bis	$5,$6,$8
	stq	$8,-16($16)
	sll	$4,$7,$2

	addq	$17,32,$17
	bis	$1,$2,$8
	stq	$8,-8($16)

	bgt	$18,.Roop

.Rend:	srl	$4,$19,$8
	stq	$8,0($16)
	ret	$31,($26),1
	.end	mpihelp_rshift

